WASHINGTON -- Insiders such as Edward Snowden who leak secrets about sensitive U.S. intelligence programs pose a "critical threat" to the United States, America's spy chiefs warned Congress in their annual report on global national security risks.

For the first time, the threat of unauthorized disclosures from "trusted insiders" was ranked as the second greatest potential threat to the country, after cyberattacks but ahead of international terrorism, in the document prepared by the 16 agencies that make up the U.S. intelligence community.

Those individuals aren't necessarily working with foreign intelligence agencies, the document says. Some members of Congress have all but accused Snowden of working for Russia's spy service, but no clear evidence has emerged to support the contention.

"The capabilities and activities through which foreign entities — both state and nonstate actors — seek to obtain U.S. national security information are new, more diverse and more technically sophisticated," the document says.

The report pays close attention to Snowden, a former contract employee at a National Security Agency listening post in Hawaii who began leaking thousands of NSA documents on surveillance programs to the media last spring and is now a fugitive in Russia.

"Trusted insiders with the intent to do harm can exploit their access to compromise vast amounts of sensitive and classified information as part of a personal ideology or at the direction of a foreign government," the report states. "The unauthorized disclosure of this information to state adversaries, nonstate activists or other entities will continue to pose a critical threat."

The heads of major intelligence agencies except the NSA are testifying at a hearing of the Senate intelligence committee Wednesday morning to deliver their annual roundup of terrorism, nuclear proliferation and other potential threats around the globe.

Those scheduled to testify include Director of National Intelligence James Clapper, CIA Director John Brennan and FBI Director James Comey.

Over the years, the annual “worldwide threat” hearings have broadened public understanding of Al Qaeda’s growing network, Pakistani support for Taliban fighters, nuclear developments in Iran and North Korea and other sensitive issues.

Last year, the threat of foreign-based cyberattacks were portrayed for the first time as a more acute danger than international terrorism, and that continues this year, although the growing strength of Al Qaeda-linked fighters in Syria and Iraq, and parts of North Africa, was noted in the pre-hearing statement.

"The threat of complex, sophisticated and large-scale attacks from core Al Qaeda against the U.S. Homeland is significantly degraded," the statement says, although it warns the threat to U.S. facilities overseas has increased.